1. Field of the Invention
The present invention relates to methods of making carbon materials and, more specifically, to methods of making high surface area carbon materials.
2. Description of the Related Art
One of the outstanding challenges in the field of supercapacitors is to achieve high energy density. To increase energy density in a supercapacitor, electrodes will require higher surface areas with controlled pore size distributions, thereby promoting massive charge accumulation near the electrode/electrolyte interfaces. The greatest advantage of supercapacitors over batteries is that they have high power density, enabling them to be charged in fraction of the time required to charge batteries. Some of the present applications of supercapacitors include: harvesting kinetic energy to store breaking energy in hybrid vehicles; and load leveling, i.e. delivering power above the average value when needed and to store excess power when the demand is below average. Improvements in energy density of supercapacitors could lead to widespread use where high energy density along with very high charge and discharge rates is required, e.g., in such applications as aerospace, industrial, transportation, utility, and consumer electronics.
Supercapacitors are also known as electric double layer capacitors (EDLC) or ultracapacitors. In EDLC, on application of voltage across its electrodes, charge accumulates in the form of ions at the surface of electrodes, forming an electrode-electrolyte double layer. Energy density of EDLC can be increased by increasing the charge at the surface, which depends on the accessible surface area to these ions. High surface area electrodes promote massive charge accumulation. Some of the other factors contributing to EDLC energy density are pore size, choice of electrolyte, and electrode materials. Micro pores (with a pore diameter of <2 nm) and meso pores (with a pore diameter in the range of 2 nm to 50 nm) are important for smooth propagation of solvated ions and high electrochemical properties.
Polyacrylonitrile (PAN)-based activated carbons are generally amorphous carbon with high surface area and good adsorption capacity. The activation process for PAN can be achieved by either physical or chemical approaches. Chemical activation tends to generate predominantly micro-pores with narrow pore size distribution whereas physical activation tends to generate predominantly micro and meso-pores with wide pore size distribution.
Current methods of generating carbonaceous materials through activating PAN materials results in surface areas below 2300 m2/g and relatively low pore volumes. However in applications such as supercapacitors, batteries, fuel cells, gas absorption and catalysts, surface areas of greater than 3000 m2/g would be highly desirable.
Therefore, there is a need for carbon materials exhibiting increased surface areas.